The camera show a good picture during the day and a bad picture at night ?

First thing to think about in this case to review your adapter ; You should replace it to increase the Ampere value supplied to the camera; because the camera consumes more electricity in night compared to day time specifically for infrared feature.

Camera image contains noise?

If cameras connected to coaxial cable; then check that there is no nearby electricity cables because coaxial cable and thereby camera image will be highly affected high voltage electricity.